The invention relates to a precision balance with a scale on top. Such balances are known e.g. from German utility model No. G 85 05 720, in which the penetration of foreign bodies into the measuring system is prevented in that the balance scale carrier, which is extended without contact through an opening in the housing, is surrounded by a membrane which bridges the free area between the balance scale pin and the opening in the housing. The membrane, in the form of a thin plastic skin, should on the one hand exhibit sufficient inherent strength to repel spray water, deleterious media or foreign bodies, yet, on the other hand, in the case of high-resolution precision balances, be as thin as possible and this as free as possible of restricting force in order not to distort the result of weighing. The mutually contradictory requirements have the result that the tightness of the membrane itself and at its connection points to the housing and the balance scale pin slackens in the course of time under the influence of mechanical stress, deleterious media and temperature differences and moisture, especially spray water, penetrates into the sensitive electronic measuring system and since the membrane is located at a high position, the penetrated liquid has no possibility of leaving the encapsulated system.
Similar disadvantages are displayed by another known balance (EP-OS No. 35 579), in which the movable load carrier exhibits the form of a closed parallelepiped and encloses the bottom plate carrying the weighing system. The latter is supported by three feet and the annular openings between the support feet and the bottom plate of the load carrier are closed by rubber sleeves or rubber membranes. In order not to distort the result of weighing in the case of small maximum loads, the encapsulated weighing system must be additionally supplemented by pressure compensation means such as porous wall sections or elastic bellows.